Manufacture of electrical condensers



Dec. 25, 1945. D. A. MOLEAN 2,391,688

MANUFACTURE OF ELEGTRICAL CONDENSERS Original Filed Aug. 31, 1938 METALEL ECTRODES DIELECTRIC- SHEETS CONTAINING A I'IALOGENATED OREANICCOMPOUND AND A COMPOUND OFA WEAK ACID AND A STRONG BASE lNVENTOR D. A.McLEA/V A TTORNEV oun Patented Dec. 25, 1945 I MANUFACTURE OF ELECTRICALCONDENSERS David A. McLean, Chath -Telephone Laborato York, N. Y.,

am, N. 1., ass lgnor to Bell ries, Incorporated, New a corporation ofNew York Application November 14, 1940, Serial No.

which is a division of application Serial No.

227,652, August '31, 1938.

Divided and this application December 10, 1941, Serial No. 422,311

11 Claims.

This invention relates to electrical condensers containingnoveldielectric materials. More particularly, it relates to electricalcondensers having dielectrics containing or impregnated with halogenatedmaterials which tend to break down slightly to form halogen acids andalso containing substances which tend to increase the life of thedielectric. This application is a division of the application of DavidA. McLean, Serial No. 365,642,

filed November 14, 1940, which is a division of theapplication of DavidA. McLean, Serial No. 227,-

. 652, filed August 31, 1938.

It has been found that certain halogenated substances or moreparticularly, certain halogenated organic compounds, chiefly halogenatedaromatic or cyclic hydrocarbons such as the chlorinated hydrocarbons,chlorinated naphthalene and chlorinated diphenyl, are very desirablematerials for condenser dielectrics. Ordinarily they are employed byimpregnating them in porous spacers such as paper, textiles or othercellulosic.materials. The resultant dielectrics possessa high dielectricconstant, high resistance, low dielectric loss and high chemicalstability.

According to the present invention, it has been found that the life ofcondensers containing this type of dielectric can be considerablyprolonged and that the ultimate failure of the dielectric, particularlywhen the condensers are operating under direct current potentials and atelevated temperatures, can be postponed by incorporating in thedielectric materials which act as stabilizers for the halogenatedmaterials.

The ultimate failure of the dielectric appears to be due todisintegration of the compounds com- I prising it. Inspection of animpregnated paper dielectric of this type after failure shows it to bespotted with carbonized and decomposed areas.

Although the invention is not to be limited to any theory of operation,it is believed that the failure of the dielectric is due to the factthat the halogenated dielectric materials, such as chlorinatednaphthalene and chlorinated diphenyl, although they are ordinarilyconsideredstable, tend to decompose slightly, particularly under theinfluence of an electrical field, to form traces of halogen compounds,chiefly hydrohalogen acids, such as hydrochloric acid. Thisdecomposition process is autocatalytic in that the trace of hydrohalogenacid formed tends to accelerate the further decomposition of thehalogenated com- The presence of this hydrohalogenacid, which acts as anelectrolyte, decreases the resist ance of the dielectric in the areas inwhich it is concentrated and, in the case of an impregnated paperdielectric, the combined electrical and chemical action causes thedestruction of the cellulose of the paper spacer.

The presence of free acid is also objectionable because it causescorrosion of the metal electrodes. When aluminum electrodes areemployed, as is often preferable, reactions involving traces ofhydrochloric acid are particularly objectionable since the aluminumtogether with the hydrochloric or other hydrohalogen acid forms aluminumchloride or other aluminum halide. Aluminum chloride, for example, isknown to be a catalyst for the destruction of halogenated organiccompounds and, therefore, causes the formation of additionalhydrochloric acid. Both the aluminum halide-and the hydrohalogen' acidact to cause the breakdown of the cellulose in the paper spacer andconsequent failure of the dielectric.

It is an object of the present invention to increase the life ofcondenser dielectrics containing halogenated materials. Broadly this isaccomplished by incorporating in the dielectric a substance capable ofreacting with the generated hydrohalogen acids to form substantiallyinert and preferably non-electrolyte substances. Only very small amountsof these materials are required to be added since, if the small amount.of generated acid is neutralized or rendered inactive, the autocatalyticaction of the acid is prevented so that the decomposition of thehalogenated substances is much less rapid.

The manner in which the present invention may be applied to condensersmay better be understood by reference to the accompanying drawing whichshows a roll type condenser made up of two electrodes separated by adielectric material.

The substances used for rendering the hydrohalogen acids inactiveaccordingto the present invention are the salts of weak acids with stronbases. The salts of weak acids with stronger bases function by reactingwith the halogen acids to form a halide of the base, thereby settingfree the weak acid, both of which resulting substances are substantiallyinert. However, since these salts are electrolytic to a mild degree, itis desirable that the amount added be kept below about 2 per cent, ingeneral, to prevent an impairment of the electrical properties of thedielectric. Preferably the amounts of added salts lie between about .2per cent and about 2 per cent. The neutralizing salts are preferablysalts of alkali metals 0r of alkaline earth metals, such as sodium,potassium, lithium, calcium, magnesium or strontium, with weak organicor inorganic acids such as boric acid,

carbonic acid, oxalic acid or acetic acid or with the very weaklyionizable organic acidsubstances contained in pectin, gum arable, cherrygum or other carbohydrate gums, or with the acid derivatives of thecarbohydrates such as, for" example, the gluconic or uronic acids.Carbohydrates, which contain hydrogen atoms of very weakly acidic naturein that they are replaced by the basic metals upon reaction withhydroxides of these metals, may also be employed in the form I ofcompounds with these basic metals. Since the pectins, gums andcarbohydrates are the least ionizable of the available substances, saltsof these substances are the preferable ones. For

economic reasons, the metallic compounds with gum arabic, particularlythe calcium compounds with gum arabic are preferable; The commercialgums and pectins available on the market ordi= narily contain smallamounts of metallic constituents, chiefly calcium and magnesium, in or=ganic combination with their acid constituents. Howeverfpreferably theyare enriched in these metallic constituents before being added to thedielectric. 'They should contain at least about l per cent of metallicconstituents and preferably about 3 per. cent or more. Although ingeneral the salts of a weak acid with a strong base should not be addedto the dielectric in an amount greater than about 2 per cent,nevertheless, when a compound of a base with a pectin, a gum or acarbohydrate isused, the substance may be added in amounts between about.2 per cent and about 5 per cent.

The stabilizers above referred to may be added to the dielectric in anysuitable manner. For instance, when a porous spacer such as paper, atextile or other celelulosic material is employed, it may be impregnatedwith a solution or suspension of the stabilizer in water or othersuitable medium.

When a paper spacer is used the stabilizer may conveniently beincorporated in the paper pulp prior to the formation of the papersheet. This is a desirable method of incorporating the soluble saltssince soaking of the finished paper in material, such as paper, andplacing the desired number of dielectric sheets between two or moremetal sheets. The alternate layers of dielectric and metal electrodesmay then be rolled into the condenser shown in Fig. l and impregnatedwith the halogenated impregnating medium. The condenser may then beplaced in a protecting case or otherwise utilized as desired.

. As a specific example of the formation of a condenser by th s method,several sheets of thin linen condenser paper are soaked in a l per centaqueous solution of gum arabic containing about 5 per cent calcium inorganic combination. After the sheets have become thoroughly aturatedthey are removed and passed through heated rolls to remove the excesssolution and dry the paper. A

condenser is then formed in the usual manner using the paper as adielectric and aluminum sheets as electrodes. The condenser is thenimpregnated by a su table process, such as vacuum aeaeee pregnated, thecondenser is removed and allowed to cool;

Obviously the impregnation or the paper with e gum arabic and thesubsequent drying may take place as a continuous procedure by passing acontinuous sheet of paper from a roll through the impregnating bath andsubsequently through a series of rolls.

A similar procedure may be employed with solutions of other stabilizingsalts. For example, a 8 per cent solution of calcium gluconate may beemployed in place of the gum arabic solution. Chlorinated diphenyl maybe employed as the halogenated impregnant with either of theabovernentioned procedures. Alternatively, water soluble materials suchas calcium giuconate or gum arabic containing about 5 per cent calciumin organic combination are incorporated in a linen paper pulp in anamount surhcient to give about 2 per cent of the stabilizer in thefinished paper. The pulp is then formed into a sheet, dried andcalendered according to the usual procedure for making paper. The paperis then formed into a condenser as described above and impregnated withchlorinated naphthalene or chlorinated diphenyi.

In place of incorporating the water-soluble materials in the pulp priorto the formation of the sheet, solutions of these materials may besprayed on the sheet formed from the pulp prior to drying. Thus gumarabic containing about 5 per cent calcium in organic combination,calcium gluconate, calcium acetate, magnesium acetate, or similarmaterials may be dissolved in water and sprayed upon a sheet of linenpaper before it passes through the drying rolls. They are used inconcentrations and amounts sumcient to insure the desired concentrationin the finished sheet. for instance about 2 per cent.

Although the invention has been described in its more specific aspects,it is to be understood that it is of broad application and is notlimited to any theory of operation, the scope of the invention beinglimited only by the scope of the appended claims.

What is claimed is:

l An electric condenser comprising metal -armatures separated by adielectric comprising a chlorinated aromatic hydrocarbon which tends tobreak down to form hydrogen chloride during the operation of thecondenser at elevated temperatures and a relatively small amount of acompound of calcium with the acidic constituents of gum arabic.

2. An electric condenser comprising a pair of electrodes separated by adielectric comprising a halogenated aromatic hydrocarbon which tends tobreak down to form a hydrohalogen acid during the operation of thecondenser at elevated temperatures and a relatively. small proportion ofgum arabic containing a strong inorganic base combined with its acidicconstituents.

3. Anelectric'condenser comprising a pair of electrodes separated byadielectric comprising a halogenated aromatic hydrocarbon which tends tobreak down to form a hydrohalogen acid during the operation of thecondenser at elevated temperatures and a relatively small proportion ofa carbohydrate gum containing a strong inorganicbase combined with itsacidic constituents.

4. An electric condenser comprising a pair of impregnation, withchlorinated naphthalene des separated by a dielectric comprising onenesschlorinated naphthalene and a, relatively small proportion of a compoundor the acidic constituents of a. carbohydrate gum with a stronginorganic base.

5. An electric condenser comprising a pair of electrodes separated by a,dielectric comprising chiorinateddiphenyl and a. relatively smallproportion of e compoundot the acidic constituents of e carbohydrate gumwith a strong inorganic ioase.

6. An electric condenser comprising metal armatures separated by adielectric containin chlorinated naphthalene and a relatively smallproportion of gum arabic containing calcium combined with its acidicconstituents.

7. An electric condenser comprising metal on matures separated by adielectric containing chlorinated diphenyl and a relatively smallproportion of gum erabic containing calcium combined with its acidicconstituents.

8. A condenser dielectric comprising Piper impregnated with e.chlorinated aromatic hydrocarbon and containing a carbohydrate gumhaving its acidic constituents combined with a strong inorganic base.

9. A condenser paper for to condenser dielectrics comprising papercontaining a compound of a strong inorganic nose with the acidsubstances contained in a carbohydrate sum.

10. A condenser paper for forming condenser dielectrics comprising papercontaining a, compound of a, strong inorganic base with the acidsubstances contained in gum arable.

11. A condenser dielectric comprising paper impregnated with e,chlorinemcl aromatic hydrocarbon and containing a small proportion ofgum arabic containing calcium combined with its acidic constituents.

DAVID A. McLEAN.

